Pressure cooker for microwave ovens

ABSTRACT

A pressure cooker for use in microwave ovens includes a microwave permeable bowl shaped container, a microwave permeable dome cover, and a steel locking ring permanently attached to the cover for maintaining the container and cover in fluid-tight seal during use. A safety valve, formed of flexible tubing, encounters a projection of the container and is deformed into a closed configuration responsive to movement of the cover, relative to the container, toward a locking position. A pressure regulator valve, consisting of a metal core surrounded by an elastically deformable casing, is positioned over a pressure control opening in the cover to maintain a selected operating pressure level in the pressure cooker. A pressure indicator and relief assembly, contained in a pressure release opening through the cover, indicates positive pressure in the chamber and is ejected in the event of an abnormally high pressure inside the housing.

BACKGROUND OF THE INVENTION

This invention relates to preparation of food, and more particularly toan apparatus for pressure cooking food items in microwave ovens.

Pressure cookers are well known for their capacity to impart a highlydesirable tenderness, texture and flavor to certain prepared foods,particularly meat. Pressure cookers usually include a bowl-shapedcontainer or base open at the top for receiving food, and a top coverfor closing the container. Because they utilize a positive pressure,these appliances must be equipped with certain features not required byother cooking utensils. For example, means must be provided formaintaining the container and cover in a fluid sealing engagement formaintenance of positive pressure. A valve is needed for maintaining aselected level of positive pressure. The cooker also should have aback-up pressure release valve, in case there is a malfunction in thepressure regulating valve. Finally, it is desirable to have auxiliaryvalve means for preventing positive pressure build-up unless the coverand container are properly engaged, and for rapid pressure release inthe event of an attempt to open the pressure cooker prior to asufficient release of positive pressure.

A pressure cooker container and top may be threadedly engaged, asdisclosed in U.S. Pat. No. 4,490,597 to Mengel granted Dec. 25, 1984. Amore convenient opening and closing arrangement is shown in U.S. Pat.No. 2,622,187 to Welch granted Dec. 16, 1952, in which the container andcover each are provided with ledges, which interlock with one anotherresponsive to rotation of the cover. A gasket is provided to completethe seal. Welch utilizes the cover weight as a pressure regulator valve,while Mengel discloses a spring loaded regulator valve. Mengel alsoshows a safety relief button which, when pressed by the user, vents thepressure cooker.

U.S. Pat. No. 4,024,982 to Schultz granted May 24, 1977 discloses a ringrotatably mounted with respect to the cover or lid of a pressure cooker.The ring is equipped with handles for rotating it 180° between its openand closed positions. A valve seating, mounted in the lid, has a valvecone that remains open until the ring is rotated to the closed position,thus to prevent a pressure build-up unless the cooker is properlyclosed. An alternative structure, shown in U.S. Pat. No. 4,103,801 toWalker granted Aug. 1, 1978, includes a sealing plug in a cover ventopening. The plug is positioned so that it can rise to permit a pressurebuild-up only when a lock member is in its proper position.

Pressure cookers designed for use in microwave ovens are intended toafford the above-mentioned advantages of pressure cooking along with theconvenience and speed of microwave cooking. These advantages give riseto certain structural requirements not heretofore adequately addressed.For example, it is desirable in microwave pressure cooking to constructthe container and cover of a microwave permeable material. Yet, suchmaterials do not lend themselves to the positive yet convenient closuredesired for pressure cookers. The valves presently used to preventpressure build-up prior to a proper seal are more complex thannecessary, and often utilize metal springs and other components notsuitable in microwave environment. Moreover, the characteristicallysmaller size of microwave pressure cookers raises the need to ensurethat large, flat, bulky food items, for example lettuce and cabbage, donot interfere with operation of the pressure regulator valve or safetypressure release valve.

Therefore, it is an object of the present invention to provide a meansfor the convenient and releasable sealing of a pressure cooker cover andcontainer, particularly when these components are constructed of amicrowave permeable material.

Another object of the invention is to provide a simple and reliablemeans to prevent positive pressure in a pressure cooker chamber unlessthe cover and container are correctly engaged.

Another object is to provide a means for rapidly releasing pressure froma pressure cooker during an attempt to disengage the cover and containerbefore the positive pressure has subsided.

Yet another object is to provide structure for preventing food items ina pressure cooker from blocking or otherwise interfering with pressurerelief openings.

And, it is an object of the present invention to provide a pressurerelief valve and auxiliary safety valve which are easily removed fromthe pressure cooker for inspection or cleaning.

SUMMARY OF THE INVENTION

To achieve these and other objects, there is provided a pressure cookerwith a housing including a container open at its top and a cover adaptedfor a sealing engagement with the top of the container to close thehousing. A valve opening is formed through the cover, and a fasteningmeans releasably maintains the container and cover in the sealingengagement responsive to movement of the cover, relative to thecontainer, to a locking position. A flexible valve means, mounted withrespect to the valve opening, provides a fluid path between the interiorand exterior of the housing. The valve means has a valve portionextended into the interior. The pressure cooker further includes atleast one closure projection integral with the container. The valveportion is positioned to contact one of the closure projections as thecover is moved toward the locking position. Responsive to furthermovement of the cover towards the locking position, the valve meanselastically deforms to close the fluid path and permit the maintenanceof a positive pressure in the housing interior.

One feature of the invention resides in the fact that the valve portiondoes not contact a closure projection, and thus does not deform to closethe fluid path, unless proper sealing engagement occurs between thecontainer and cover. If the pressure cooker is not properly closed, thevalve means provides a fluid path for steam and vapor to escape,preventing build-up of positive pressure inside the housing.Furthermore, as the cover is moved away from the locking position toopen a closed pressure cooker, it carries the valve means away from theclosure projection and re-opens the fluid path, permitting rapid escapeof steam and vapor to reduce any positive pressure. This protects a userwho mistakenly attempts to open the pressure cooker before pressure hassubsided. The preferred valve means is a cylindrical length of tubingremovably and frictionally mounted within the valve opening of thecover. Such tubing is readily removed for inspection or cleaning.

Another aspect of the present invention is a pressure cooker adapted foruse in microwave ovens. The pressure cooker has a bowl-shaped containeropen at the top, constructed of a microwave permeable material andhaving an annular upper rim. A microwave permeable cover is provided,with an annular cover rim adapted for a sealing engagement with theannular upper rim of the container. A fastening means releasably joinsthe container and cover when in the sealing engagement. The fasteningmeans includes a plurality of spaced apart first latching membersintegral with the cover and arranged about the cover rim. A plurality ofspaced apart second latching members are integral with the container andarranged about the upper rim. The second latching members are positionedto allow each of the first latching members to descend between and belowan associated pair of the second latching members as the cover is placedin the sealing engagement upon the container. Rotation of the cover withrespect to the container, with the container and cover so engaged, moveseach of the first latching members into an interlocking engagement withone second latching member of the associated pair. This forms aplurality of interlocked pairs, each including one first locking memberand one second locking member. One locking member of each interlockedpair is constructed of a microwave permeable material, while the otherlatching member of the pair is constructed of metal.

Preferably, all of the first latching members are constructed of steel,and comprise part of a steel ring permanently attached to the cover rim.Consequently, with the container and cover microwave permeable, thesteel ring provides the necessary tensile strength to permit use of theinterlocking latching members to conveniently secure the cover andcontainer.

A further aspect of the present invention is a pressure cookingapparatus including a housing, a generally cylindrical pressure releaseopening extended longitudinally through a wall of the housing from theinterior to the exterior of the housing, and an elastically deformablegenerally cylindrical plug removably contained in the pressure releaseopening. The plug has a nominal diameter, with first and second radiallyoutwardly extended flanges at opposite ends of the plug. The pressurerelease opening includes a medial portion having a diametersubstantially equal to the nominal diameter, a first radially enlargedend portion at the housing exterior to accommodate the first flange, anda second radially enlarged portion at the housing interior toaccommodate the second flange. An annular surface portion of the housingwall which forms the boundary between the medial portion and the secondradially enlarged portion is inclined radially outward andlongitudinally away from the surface.

Due to the inclination of the boundary surface portion, annular linecontact is created between the boundary surface portion outer edge andthe second flange of the plug. This results in a higher chamber pressurelevel before the plug is ejected, and also a more consistent ejectionpressure level, as compared to a transverse orientation of such boundarysurface portion.

Preferably, a plurality of relief elements are formed in the housinginterior surface near the pressure release opening. This prevents large,relatively flat and deformable food items such as lettuce, from blockingthe pressure release opening.

IN THE DRAWINGS

For a better appreciation of these and other features and advantages,reference is made to the following detailed description and theaccompanying drawings, in which:

FIG. 1 is a front elevation of a pressure cooker constructed inaccordance with the present invention;

FIG. 2 is a top plan view of the pressure cooker of FIG. 1;

FIG. 3 is a bottom plan view of a cover of the pressure cooker;

FIG. 4 is a partial top view of the pressure cooker with the coverremoved;

FIG. 5 is a partial interior side elevation of a container of thepressure cooker;

FIG. 6 is a side view of pressure relief safety valve removed from thecover;

FIG. 7 is a sectional view taken along the line 7--7 in FIG. 2;

FIGS. 8a-8c illustrate operation of the pressure relief safety valve andclosure projection;

FIG. 9 is a sectional view taken along the line 9--9 in FIG. 2;

FIG. 10 is a sectional view taken along the line 10--10 in FIG. 2; and

FIG. 11 is a view similar to that of FIG. 10, but with a positivepressure inside the pressure cooker.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Turning now to the drawings, there is shown in FIG. 1 a pressure cooker16 particularly well adapted for use in microwave ovens. The pressurecooker has a housing including a bowl-shaped container 18 open at itstop for receiving food, and a cover 20 in the shape of a dome andadapted for sealing engagement with container 18 to close the pressurecooker and enable maintenance of a positive pressure inside the housing.Container 18 and cover 20 preferably are formed of a thermoset polyesterresin, or other material permeable to microwave energy.

Formed as an integral part of container 18 are a plurality of feet 22for supporting the container with respect to a counter or the floor ofthe microwave oven, not shown. Handles 24 and 26 are provided onopposite sides of the container near its top. Near the periphery ofcover 20 is a cut-out 28 for accommodating a pressure relief safetyvalve which extends through the cover. A flat landing 30 is formed atthe center of cover 20, and supports a pressure indicator and releaseassembly including a plastic stem or poppet valve 32 and a silicone plugor grommet 34 supporting the stem and contained in an opening throughcover 20. A stand 36, extending upwardly from landing 30, supports apressure control valve 38. Extended radially outward from landing 30, inopposite directions, are first and second wings 40 and 42, formed aspart of cover 20 and enabling convenient manual rotation of the coverwith respect to container 18, about a vertical axis. A steel lockingring 44, permanently mounted to cover 20, secures the cover andcontainer in their sealing engagement as is later explained.

As seen in FIG. 2, locking ring 44 is provided with a rectangular notch46. A rise 48 in cover 20, of a size and shape similar to notch 46, fitssnugly within the notch to ensure a proper angular alignment of ring 44with cover 20 prior to its permanent attachment. First and secondmarkers 50 and 52, each formed as a raised portion on cover 20, indicatewhether the cover, relative to container 18, is in its open unlocked orlocked angular position. More particularly, first and second handlemarkers 54 and 56 are provided on handles 24 and 26, respectively. Thealignment of second marker 50 with either handle marker indicates thatthe pressure cooker is properly locked, while the alignment of marker 52with either handle marker indicates the closed, but unlocked position.

A pressure relief safety valve 58 extends through cover 20 to providefluid communication between the interior and exterior of the pressurecooker, by means of a pressure relief orifice 60 through the valve.

FIG. 3 shows the bottom or inside surface 74 of cover 20, to reveal sixlatching members 62 forming a part of locking ring 44 and extendedradially inward from the remainder of the ring at the bottom thereof. Apressure release opening 64 contains grommet 34 and poppet valve 32during use of the pressure cooker, but these components are readilyremoved from opening 64 for cleaning or inspection. Near opening 64 is asmaller pressure control opening 66, likewise extended through thecover.

A plurality of relief elements or raised portions are formed into cover20 proximate openings 64 and 66, including five relatively short reliefelements 68, and a pair of parallel spaced apart ribs 70 and 72 extendedfrom the cover periphery to a point near the pressure release opening.These relief elements prevent relatively large, flat and pliable fooditems, for example leaves of lettuce or cabbage, from lying against thecover inside surface 74 to block or otherwise interfere with openings 64and 66.

A rim 76 of cover 20 is specially shaped to accommodate an annulargasket used to seal the cover and container 18. Formed near rim 76 is aboss 78 through which is formed valve opening 80 for containing safetyvalve 58.

In FIG. 4, a portion of container 18 is shown in top view with cover 20removed, in order to show an upper rim 82 of the container, and part ofan annular gasket 84 which fits into a groove 86 formed in upper rim 82and into a corresponding groove in the cover to effect a positive fluidseal between container 18 and cover 20 when the pressure cooker islocked. A sealing ridge 87 in groove 8 cooperates with gasket 84 to sealthe housing. Also shown at 88 is one of six container latching members,each of which extends radially outward from upper rim 82, and is adaptedfor an interlocking engagement with one of latching members 62 oflocking ring 44. Like latching members 62, container latching members 88span approximately 30° of angular rotation, and are spaced apart fromeach other approximately 30°.

As seen from FIGS. 4 and 5, a closure projection 90 extends radiallyinwardly from the inside surface 92 of container 18. The closureprojection spans most of the container height, but is particularlyuseful in that it provides an inclined camming surface 94 which extendsupwardly at an angle of approximately 45°, and a horizontal retaining orcrimping surface 96 adjacent the upper end of the camming surface. Asubstantially identical second closure projection, not shown, extendsradially inwardly from inside surface 92 opposite closure projection 90,i.e. angularly spaced apart 180°.

Safety valve 58, shown as removed from valve opening 80 in FIG. 6, has acylindrical body 98 of a nominal diameter, for example 0.25 inches. Atthe top of valve 58 is a radially outwardly extended flange 100. Anindicator ring 102 is formed in the valve near its longitudinal center.Approximately midway between ring 102 and flange 100 is an annularraised portion 104 designed to frictionally secure valve 58 within valveopening 80. Pressure relief orifice 60, formed longitudinally throughthe valve, has a diameter of 1/8 inch.

FIG. 7 shows safety valve 58 contained within valve opening 80 of cover20 and crimped between boss 78 and closure projection 90. Flange 100rests within a radially enlarged portion on a ledge of the opening. Theremainder of opening 80 has a diameter substantially the same as thevalve nominal diameter. As a result, raised portion 104 is elasticallycompressed and thus frictionally maintains valve 58 within opening 80.Indicator ring 102 lies just below the bottom or inside surface of boss78. When a user, having inspected or cleaned safety valve 58, re-insertsthe valve into opening 80, ring 102 emerges from the bottom of theopening to indicate that the valve has been properly inserted.

Also seen in FIG. 7 is the manner in which each latching member 62 oflocking ring 44 interlocks with an associated one of container latchingmembers 88 to secure the sealing engagement of the container and cover.Six container latching members, each spanning approximately 30° arc, aresymmetrically arranged about upper rim 82. Similarly, latching members62 are symmetrically arranged on locking ring 44. The latching membersare so arranged, that when cover 20 is placed upon container 18 withfirst marker 50 aligned with either handle marker, each latching member62 descends between an associated pair of container latching members 88,to a point below the associated pair. Rotation of cover 20, relative tocontainer 18 toward the locking position, moves each of latching members62 into an interlocking engagement with one of its associated containerlatching members 88, namely the one to its clockwise side as viewed inFIG. 2. Thus, with cover 20 in the locking position, six interlockingpairs are formed, each pair including a latching member 62 and acontainer latching member 88.

With the cover and container locked together, gasket 84, responsive to apositive pressure inside the housing, elastically deforms to provide afluid tight seal between the cover and container. More particularly, anannular sealing ridge 105 is formed in a groove 107 in rim 76, radiallyaligned with ridge 87. The free ends of generally C-shaped gasket 84 aredirected radially inward as shown in FIG. 7, each end associated withone of ridges 87 and 105. A positive pressure inside the housing urgesthe annular end portions of gasket 84 away from one another, pinningeach against its associated sealing ridge to form the required seal. Toenhance the seal, each of ridges 87 and 105 has opposite, inclined sidewalls converging to a sealing edge. Because each sealing edge isrelatively sharp, its associated end portion is bent around it,responsive to positive pressure, in a wrapping engagement to improve theseal. The edges are not so sharp, however, as to cause any damage togasket 84.

As cover 20 is rotated into its locking position, safety valve 58 iscrimped to close off the fluid path provided by orifice 60. Thiscrimping or closure of valve 58 is illustrated in FIGS. 8a-8c. FIG. 8ashows the position of safety valve 58--including a valve portion 106 ofthe valve extending into pressure cooker 16--relative to closureprojection 90 after some movement of cover 20 toward its lockingposition. In FIG. 8b, as the cover is further rotated toward its lockingposition, valve portion 106 is carried into contact with camming surface94 of the closure projection and is bent. Finally, with cover 20completely locked, boss 78 has been carried rightward beyond themajority of retaining surface 96, leaving valve portion 106 trailing andheld between the boss and retaining surface, crimped sufficiently toclose the fluid passage otherwise provided by the valve orifice.

It can be appreciated that a substantially identical locking sequencewould occur between valve 58 and the other closure projection. Shouldcover 20 initially be improperly positioned on container 18, safetyvalve 58 would not encounter either closure projection during locking.Hence, pressure relief orifice 60 would remain open, preventing apositive pressure build-up following such improper closure.

Safety valve 58 also can protect an operator who attempts, improperly,to open the pressure cooker before positive pressure has subsided. Fromconsidering FIGS. 8a-8c in a reverse sequence, it is understood thatunlocking cover 20 involves moving boss 78 and valve 58 leftward asviewed in these figures. The arcuate dimensions of latching members 62and cover latching members 88 are selected such that they remain atleast partially interlocked even with valve portion 106 free of cammingsurface 94 as pictured in FIG. 8a. Valve 58 is made of a silicone withsufficient elastic memory properties to rapidly restore the valve to itsnormal configuration. A silicone with a durometer of about 50 has beenfound satisfactory. As a result, steam and vapor quickly escape throughorifice 60, depleting the positive pressure.

FIG. 9 shows stand 36 extended from flat landing 30. Running through thestand and through the remainder of cover 20 is a pressure controlorifice 108. Pressure control valve 38 includes an annular metal core110 surrounded by a polymer casing 112. A nodule 114 is formed in thecasing, and normally rests inside pressure control orifice 108 aspressure control valve 38 is supported by stand 36. A sufficientbuild-up of positive pressure in the pressure cooker, however, forcescontrol valve 38 to temporarily rise, permitting escape of steam andvapor. The weight of control valve 38 is selected to permit the escapeof steam and vapor whenever the pressure inside the pressure cookerexceeds a predetermined level, for example ten pounds per square inch.Casing 112 protects stand 36 from any damage from the impact of valve 38as it falls upon the stand and vibrates against it.

FIG. 10 shows the pressure relief assembly including grommet 34 andpoppet valve 32 housed in pressure release opening 64 of the cover. Acentral bore 116 through the grommet has a flared portion 118 at thebottom to receive an enlarged base 120 of pressure indicator poppetvalve 32. Valve 32 has an enlarged top portion 122 which maintains thevalve within grommet 34.

Grommet 34 has a nominal diameter of 0.625 inches, with radiallyoutwardly extended upper and lower flanges 124 and 126, respectively.Release opening 64, in turn, has a first radially enlarged portion atthe cover outside surface to accommodate flange 124, and a secondradially enlarged portion 130 at inside surface 74 to accommodate flange126. An annular boundary 132 between enlarged portion 130 and the medialpart of opening 64 is inclined, radially outward and upwardly(longitudinally) away from inside surface 74. As a result, flange 126 isbent upwardly responsive to positive pressure, as shown in FIG. 10. Alsoin response to positive pressure, base 120 becomes seated in flaredportion 118 of bore 116, raising enlarged top 122 above grommet 34, toprovide to the user a visual indication of a positive pressure insidethe pressure cooker. Due to the incline of border or boundary 132,grommet 34 is prevented from a premature ejection. At the same time,should there be a severe rise in positive pressure due to a malfunctionof pressure control valve 38, grommet 34, and valve 32 are forcedupwardly out of pressure release opening 64. In practice, the normaldesired internal pressure is ten pounds per square inch, and the grommetis fashioned to exit the pressure relief opening when the internalpressure exceeds twenty pounds per square inch.

Thus is disclosed a pressure cooker particularly well suited for use inmicrowave ovens. The grommet 34 acts as a safety valve and is releasedin the event of excessive pressure. By contrast, the poppet valve risesresponsive to even slight positive pressure to indicate its presence.The steel locking ring and polyester resin latching members provide aconvenient and secure seal between the cover and container, yet alsopermit the cover and container to be constructed of microwave permeablematerial. The safety valve, in an inexpensive, simple and reliablemanner, prevents positive pressure build-up unless the cover is properlylocked against the container, and further allows rapid escape of steamand vapor in the event of an attempt to unlock and remove the coverbefore positive pressure has subsided.

What is claimed is:
 1. A pressure cooker including:a housing including acontainer open at its top and a cover adapted for a sealing engagementwith said container to close the housing, means forming a valve openingthrough said cover, and a fastening means for releasably maintainingsaid container and cover in said sealing engagement responsive tomovement of said cover, relative to said container, to a lockingposition; a flexible valve means, mounted with respect to said valveopening, for providing a fluid path between the interior and exterior ofsaid housing, said valve means including a valve portion extended intosaid interior; and at least one closure projection integral with saidcontainer; said valve portion being positioned to contact one of saidclosure projections as said cover is moved toward said locking position;and, responsive to further movement of said cover toward the lockingposition, elastically deforming to close said fluid path and permit themaintenance of a positive pressure in said housing interior.
 2. Thepressure cooker of claim 1 wherein:said valve means comprises agenerally cylindrical length of tubing removably and frictionallymounted within said valve opening, with said valve opening located atthe periphery of said cover, and with each closure projection located atthe periphery of said container.
 3. The pressure cooker of claim 2wherein:said valve opening has a ledge near the outside surface of saidcover, and said tubing includes a flange at one end thereof adapted forseating engagement against said ledge.
 4. The pressure cooker of claim 2wherein:said tubing has an annular raised portion contained in saidvalve opening when said flange is so engaged, the outside diameter ofsaid annular portion being larger than the diameter of said valveopening.
 5. The pressure cooker of claim 4 wherein:said tubing has ameans for providing a visual indication, at the inside surface of saidcover, that said flange is so engaged.
 6. The pressure cooker of claim 5wherein:said tubing has a durometer of approximately
 50. 7. The pressurecooker of claim 1 wherein:each of said closure projections includes aninclined camming surface initially encountered by said conduit portionduring said movement toward said locking position, and a horizontalretaining surface for maintaining said valve portion in a deformed, pathclosing configuration.
 8. The pressure cooker of claim 1 wherein:saidfastening means includes a plurality of spaced apart first latchingmembers integral with said cover and arranged about the cover periphery,and a plurality of spaced apart second latching members integral withsaid container and arranged about an upper rim of said container, saidsecond latching members positioned to permit each of said first latchingmembers to descend between and below an associated pair of secondlatching members as said cover is seated upon said container, saidmovement of said cover toward said locking position moving each firstlatching member into an interlocking engagement with one of saidassociated pair of second latching members to form a plurality ofinterlocked pairs, each pair consisting of one first latching member andone second latching member.
 9. The pressure cooker of claim 1including:a pressure control opening formed through said cover, and apressure control valve member including a metallic core surrounded by anelastically deformable casing, said casing including a nodule normallyinserted into said pressure control opening; the weight of said core andcasing and the diameter of said nodule being selected such that saidvalve member is lifted away from said pressure control opening wheneverthe pressure in said housing interior exceeds a preselected level. 10.The pressure cooker of claim 1 wherein:said cover and container areconstructed of a microwave permeable material.
 11. The pressure cookerof claim 1 including:a gasket, generally C-shaped in cross-section andhaving two opposite end edge portions; means forming a first groove insaid cover and a second groove in an upper rim of said container; and afirst ridge in said first groove and running the length thereof, and asecond ridge in said second groove and running the length thereof;wherein said gasket, with said cover in said locking position, iscontained between said first and second grooves, with each of said endedge portions lying against an associated one of said ridges; a positivepressure in said housing causing each end edge portion to elasticallydeform about its associated ridge to effect said sealing engagement. 12.A pressure cooker adapted for use in a microwave oven comprising:abowl-shaped container open at the top, constructed of a microwavepermeable material and having an annular upper rim; a microwavepermeable cover having an annular cover rim adapted for a sealingengagement with the annular upper rim of said container; and a fasteningmeans for releasably joining said container and cover in said sealingengagement, said fastening means including a metal locking ringsurrounding and permanently attached to said cover at said cover rim andextended below said cover rim, said ring having a plurality of spacedapart first latching member arranged about a bottom portion of saidlocking ring and extended radially inwardly thereof; and a plurality ofspaced apart second latching members integral with said container,arranged about the upper rim, and constructed of a microwave permeablematerial; said second latching members positioned to allow each of saidfirst latching members to descend between and below an associated pairof said second latching members as said cover is placed in said sealingengagement upon said container, rotation of said cover with respect tosaid container, with said container and cover so engaged, moving each ofsaid first latching members into an interlocking engagement with onesecond latching member of said associated pair, thus to form a pluralityof interlocked pairs, each interlocked pair including one first latchingmember and one second latching member.
 13. The pressure cooker of claim12 wherein:said locking ring is formed of steel.
 14. The pressure cookerof claim 13 including:means forming a notch in said ring, and a rise insaid cover having a size corresponding to the size of said notch, forangularly aligning said ring and said cover rim prior to their permanentattachment to one another.
 15. A pressure cooking apparatus including:ahousing, a generally cylindrical pressure release opening extendedlongitudinally through a wall of said housing from the interior to theexterior thereof, and an elastically deformable generally cylindricalplug removably contained in said pressure release opening; a pluralityof relief elements formed in said interior surface and proximate saidpressure release opening; said plug having a nominal diameter, andhaving first and second radially outwardly extended flanges at itsopposite ends; said pressure release opening including a medial portionhaving a diameter substantially equal to said nominal diameter, a firstradially enlarged end portion at said housing exterior to accommodatesaid first flange, and a second radially enlarged portion at saidhousing interior surface to accommodate said second flange; and whereinan annular boundary between said medial portion and said second radiallyenlarged portion is inclined radially outward and longitudinally awayfrom said interior.
 16. The apparatus of claim 15 wherein:means form alongitudinal valve bore through said plug, and a poppet valve is movablycontained in said bore for providing, outside of said housing, a visualindication of a positive pressure inside of said housing.
 17. Theapparatus of claim 15 wherein:said housing includes a container open atthe top thereof and a cover adapted for a sealing engagement with saidcontainer to close said housing, wherein said pressure release openingextends through said cover near its center, and wherein said reliefelements include a pair of parallel, spaced apart ribs extended from theperiphery of said cover to a location near said pressure releaseopening.